How to Name a Plane in Geometry

May 2, 2024
5 min read

Discover how to name a plane in geometry. Keep reading to learn the fundamental concepts of how to identify the planes. 

In geometry, naming planes is crucial for precise communication and problem-solving. Understanding planes in geometry accurately allows for more straightforward explanations and efficient analysis of geometric figures. 

This article explores the process of naming planes. By delving into the fundamentals of plane identification, you’ll gain a deeper understanding of geometric concepts and enhance your problem-solving skills. 

What Is a Plane?

A plane is a flat, two-dimensional surface that extends infinitely in all directions. It is basically flat, like a sheet of paper. However, unlike a flat shape with edges, a plane has no thickness and continues forever. Planes are characterized by their uniformity and lack of curvature. 

Understanding planes is crucial in geometric analysis, allowing users to visualize and manipulate spatial relationships. Mastery of this concept facilitates precise problem-solving, making it an essential topic in mathematical education. Let’s see how to identify a plane in Geometry.

How to Identify a Plane in Geometry

To name a plane, three non-collinear points should be present on a two-dimensional flat surface. If points A, B, and C are present in two-dimensional flat surfaces, then we can call the plane ABC or the whole surface” P.” Hence, a plane is named by combining three non-collinear points or represented by a capital letter.

Naming Planes


The XY plane is one of the most basic planes in three-dimensional space. It has the x and y axes and contains all points with a z-coordinate of zero. Mathematically, it can be represented by the equation z = 0. This plane divides the space into upper and lower halves.


The YZ plane is perpendicular to the x-axis and defined by the y and z axes. It contains all points with an x-coordinate of zero and can be represented by the equation x = 0. This plane divides the space into left and right halves.


The XZ plane is perpendicular to the y-axis and defined by the x and z axes. It contains all points with a y-coordinate of zero. It is represented by the equation y = 0. This plane divides the space into front and back halves.

Vertical Plane

A vertical plane is perpendicular to the horizontal plane. It stands upright and extends infinitely in the vertical direction. Examples in architectural drawings include walls, doors, and windows.

Horizontal Plane

A horizontal plane is perpendicular to the vertical plane and parallel to the ground. It represents surfaces such as floors, ceilings, and tables.

Oblique Plane

An oblique plane is neither parallel nor perpendicular to the coordinate axes. It intersects the axes at oblique angles, resulting in a diagonal orientation.

Bisecting Plane

A bisecting plane divides a geometric object into two equal parts. For example, the midplane of a cube passes through its center, dividing it into two congruent halves.

Tangent Plane

In calculus, a tangent plane is a plane that touches a surface at a single point and shares the same slope as the surface at that point. It is commonly used in the study of functions of multiple variables.

Normal Plane

The normal plane to a curve at a given point is perpendicular to the tangent to the curve at that point. It helps in understanding the behavior of the curve locally.

Intersecting Planes

When two planes intersect, they form a line called the intersection line. The angle between the intersecting planes determines the orientation of the line.

These examples show how planes are named and defined based on their orientation, position, and relationship with axes or other geometric objects. Understanding these concepts is essential for solving problems in geometry.

Types of Plane

Planes in geometry encompass diverse configurations, each with unique properties and applications. It’s crucial to understand these variations. Below are examples of different types of planes:

Parallel Planes

Parallel planes are planes that do not intersect, no matter how far they extend. They have a constant distance between each other. Mathematically, two planes are parallel if their normal vectors are parallel. 

For example, the XY-plane and the XZ-plane are parallel because they both have the same normal vector, which is perpendicular to the Y-axis.

Perpendicular Planes

Perpendicular planes intersect at right angles. The line of intersection between two perpendicular planes is perpendicular to both planes. In three-dimensional space, examples of perpendicular planes are the XY plane and the YZ plane.

Cylindrical Plane

A cylindrical plane is formed by a straight line (axis) and a curve (base) that is parallel to the axis. The surface of a cylinder is made up of infinitely many cylindrical planes. Examples of cylindrical planes are a cylinder's lateral surface and a cone's surface.

Conical Plane

A conical plane is formed by a point (apex) and a curve (generatrix) that intersects the apex. The surface of a cone is made up of infinitely many conical planes, which are commonly seen in objects like traffic cones and ice cream cones.

Ruled Plane

A ruled plane is a surface that can be generated by moving a straight line (ruling) while keeping it parallel to a fixed direction. Examples of ruled surfaces include the surface of a cylinder and a hyperbolic paraboloid.

Principal Plane

Principal planes are planes perpendicular to the optical axis of an optical system. They simplify the analysis of optical systems by reducing the number of optical elements to be considered.

Inclined Plane

An inclined plane is basically a ramp. Picture a flat, straight surface that isn't level with the ground but instead slopes up or down. This slope forms an angle when you compare it to a flat surface, like a floor or the ground, which we think of as horizontal. It is commonly used in physics to study the effects of gravity and friction on objects sliding or rolling down a slope.

Orthogonal Plane

Orthogonal planes intersect at right angles. They are commonly encountered in engineering and architecture, where orthogonal projections represent three-dimensional objects on a two-dimensional plane.

Polar Plane

In polar coordinates, a polar plane is a plane that consists of all points with a fixed distance (radius) from a reference point (pole) and a fixed angle (polar angle) from a reference direction (polar axis).

These planes have a unique way of defining their characteristics and applications. Mastery of these concepts enables you to analyze and manipulate spatial relationships.

Properties of a Plane

The properties of planes in geometry are essential for analyzing their behavior and interactions within three-dimensional space. Here are several key properties of planes:


Planes exhibit symmetry across their normal axis. This means that if a point lies on one side of the plane, its symmetrical counterpart lies on the opposite side at an equal distance from the plane. Symmetry is a fundamental property of planes and is crucial in various geometrical contexts.


Parallel planes have a constant distance between each other and never intersect, regardless of how far they extend. This property is characterized by the parallelism of their normal vectors. For example, the XY-plane and XZ-plane are parallel to each other, as they share the same normal vector.


Perpendicular planes intersect at right angles, forming a line of intersection that is perpendicular to both planes. For instance, the XY-plane and YZ-plane in three-dimensional space are perpendicular to each other, as their normal vectors are orthogonal.

Intersecting Behavior

When two planes intersect, they form a line called the intersection line. The angle between the intersecting planes determines its orientation, which can be horizontal, vertical, or oblique.

Bisecting Property

A plane can bisect a geometric object, dividing it into two congruent parts. For example, the midplane of a cube passes through its center, splitting it into two identical halves.


A plane's inclination refers to the angle it makes with respect to a reference plane, usually the horizontal plane. This property is crucial for understanding the plane's orientation in space.

Normal Vector

Every plane has a unique normal vector perpendicular to its surface. This vector determines the plane's orientation and is instrumental in various mathematical operations involving planes, such as finding their equations and determining their intersection behavior.

Distance from Origin

The distance from the origin to a plane along its normal vector is a key property determining the plane's position in space. This distance is often represented as the constant term in the equation of the plane.

Intercept Form

The intercept form of a plane's equation represents its intersection with the coordinate axes. It provides valuable information about the plane's position and orientation in space.

Point-Plane Distance

The distance from a point to a plane is determined by projecting the point onto the plane along a line perpendicular to the plane. This property is essential for calculating distances and determining the relationship between points and planes.

These properties show how different planes can be. It also helps one's ability to analyze and manipulate planes in geometry. A thorough grasp of these properties is essential for solving complex problems.

FAQs: How to Name a Plane in Geometry

Here are answers to frequently asked questions on how to name a plane in geometry:

1. Is 2 Points Enough to Name a Plane?

No, two points are not enough to name a plane. This is because two points are insufficient to define a plane in three-dimensional space. A plane requires a minimum of three non-collinear points or a point and a non-zero vector perpendicular to it for unique identification.

2. Can 4 Points Determine a Plane?

Yes, four non-coplanar points are adequate to determine a plane uniquely. As long as the points are not all in the same plane, they can establish a unique plane passing through them.

3. How to Name a Point in Geometry?

Points in geometry are named using uppercase letters, often with subscripts for clarity. They can also be named based on their coordinates in a coordinate system, providing precise location references.

4. What Is the Equation of a Plane in 3D Space?

In three-dimensional space, the equation of a plane is represented by

Ax + By + Cz + D = 0

Where A, B, and C are the coefficients of the variables x, y, and z, respectively, and D is the constant term. This equation is derived from the plane's normal vector (A, B, C) and a point (x, y, z) on the plane.

5. How Do You Determine if a Point Lies on a Plane?

To determine if a point lies on a plane, substitute the coordinates of the point into the equation of the plane. If the resulting expression equals zero, then the point lies on the plane. 

Alternatively, you can calculate the distance between the point and the plane using the point-plane distance formula. If the distance is zero, the point lies on the plane.

6. How Are Planes Used in Real-world Applications?

Planes have numerous applications across various fields. In architecture and engineering, planes represent surfaces such as walls, floors, and ceilings in building design. In mathematics and physics, planes are fundamental geometric constructs for modeling and analyzing spatial relationships and phenomena.


From defining planes and naming points to analyzing their properties and applications, the concepts and terms explored in this article provide a solid foundation for mathematical reasoning and problem-solving. 

Note that you cannot understand spatial relationships without mastering the principles of plane geometry

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